Conventionally, in a motor drive device where a power device is required to be cooled, there is used a heat sink having a structure where a base having a flat plate shape is joined to the power device, a plurality of heat radiating fins having a flat plate shape are arranged parallel to each other at intervals on the base such that the heat radiating fins extend orthogonally to the base from a surface of the base on a side opposite to a surface of the base joined to the power device, and distal ends of the plurality of heat radiating fins are connected with each other by way of a bridge member formed by bending a metal plate in a zigzag shape (see Japanese Unexamined Patent Application, Publication No. 2001-110958 (PTL 1), for example).